Chemical process



Patented Jan. 22, 1946 unim- STATES, PATENT orrica I l A 2,303,531 I John L. Bart, Baytown, Ten, who: to Stand- Company, a corporation ard Oil Development of Delaware No Drawing. Application October 3i, 1041i,

Serial No. timid 6 Claims. (or i'ivs) The present invention relates to improvements in the preparation or synthesis of hydrocarbons boiling substantially within the gasoline range, and more particularly it relates to improved means for preventing the corrosion of distillation equipment employed in distlllling the iso-paraflln olefin alkylate.

As is known, an iso-paraflin may be reacted with an olefin to form an addition product commonly called an alkylate. That is to say, isobutane may be reacted with butylene to form a condensation product which.v is saturated andtanlr from which it is subsequently withdrawn and comparable to those used in the fractionating unit charged intoa debutanizer column. The debutanized alkylate. is then charged to a fractionating column where the butane fraction and the octanes and lighter hydrocarbons in the case of butylene alkylate or the pentane fraction and v octanes and lighter hydrocarbons in the case of pentylene alkylate are removed. The bottoms from this operation are then further reduced in a still for'removal of any fractions suitable for use in motor gasoline but .too high in boiling range for inclusion in aviation fuel.

The foregoing operation results in corrosion in the alkylate fractionating columns, in the reflux accumulators, in the transfer lines to the iractionating equipment, in the charge storage tanks, but the major corrosion has been found to occur in the fractionating column preheaters. and reboilers.

An aqueous caustlcsoda (2% caustic) followed by a water wash has been employed for the elimination of $03 in the alkylate product goingto the distillation unit'charge tank. However, the use of caustic and water wash serve only to remove 80: and entrained acid, but has not prevented the corrosion and fouling tendency oithe alkylate during subsequent handling and processing. It

is believed that decomposition or ester-sin the- 7 preheatlng and. reboiler system results in the formation of deposits and volatile acidic materials, such as 80:, since tests have indicated that u Fouling e u. F. heating the alkylate product to' reboil'ers will cause-S02 to be liberated along with a tarry material which is deposited. The product of this unstable material is not an inherent characteristic of the alkylation reaction but is probably the result of side reactions varying with operating conditions since at times the decomposition edect is most severe and at other times almost entirely negligible.

It has been found that the introduction of small quantities (about 0.01% by volume based on the debutanlzed alkylate) of inhibitors, such as tricresol or petroleum phenols, into the alkylate product has served to reduce the corrosion tendencies. In these tests the alkylate product is debutanized by flash vaporization at atmospheric temperature before adding the inhibitor. Quantities of inhibitor varying from 0.001 to 0.01% by volume (based on the debutanized alkylate) were added and the inhibited material heated to 400 F.

The vapors were tested during the heating period for S02 and the residue left after heating was tested for acidity and sulfate ion. The tests indicated that a minimum of 0.005% by volume and the maximum of 0.01% was desirable for reduction of decomposition during the heating. Tricresol and distilled crude petroleum phenols (produced by neutralization with H2804. of a B. caustic wash applied to heating oils and cracked naphthas) were found to be equally efie'ctive as inhibitors. However, although it has been found desirable to add the amount of inhibitor specified above, 0.001 to 0.1% by volume (based on the debutaniaed alkylate) may be used.

In the succeeding five tests I have set forth the results found in inhibiting a debutanized alkylate and they are asiollows:

Example 1 Alkylate debutanized, caustic and water washed and' tested by heating in glass:

'lricresol added, vol. percent Uninhibited Fouling temp,

230 None at 320 Petroleum phenols added, vol.

Uninbil Perm lied None at 320 None at 320 None at 320 Allrylate debutanized, caustic and water washed a and tested by heating in glass:

0.01 volume Uninhibitsd per cent tri- -cresol added Fouling temperature, F 320 B; in vapors .Yes No Example 4 Alkylate was debutanized, caustic and water washed and distilled with and without steam as follows:

Example 5 A sampleof alkylate was debutanized and 0.01 volume percent of a mixture of monobutyl and di-butyl sulfates added to a portion of the alkylate.

Tests in glass gave the following results:

Uninhibited +01% tria'eeol Fouling temp., I 180 None at 370. B0; in vapor, at I 150 None. 80thbottom.-..........-.-.-... 8light....-. Do.

The "triciesor above referred to is a mixture of meta, ortho and para cresols. (Vide page 956, Hackh's Chemical Dictionary 1937, published by P. Blakiston's Sons 8: Co. Inc., 1012 Walnut Street, Philadelphia, Pa.) This product is sold commerciallyas a coal tar distillate boiling around 190 to 210 C. at one atmosphere.

To recapitulate, my present invention relates to improvements in the alkylation of' iso-parafllns, and in its essence it involves treating the allwlate with a mono or polyhydric phenolic inhibitor which will decrease the tendency of the alkylate to corrode and/or foul the transfer lines, settling tanks, preheaters, reboilers, and fractionating equipment in which the raw alkylate is transferred and/or treated in order to produce a finished product. In other words, even though the raw alkylate is treated with caustic soda and later washed with water, it has been found that the thuswashed product when reboiled or reheated in distillation equipment or the small amount of inhibitor such as mono or poly- 1 hydric phenols, either alkyl substituted or unsubstituted, including tricresol, petroleum phenols,

v 40 the phenol is a monohydric phenol.

pyrogallol, resorcinol, hydroquinone and the like.

Many modifications of my invention will readily suggest themselves to those familiar with this I claim: v;

1. In an isoparaflin-olefln alkylation conducted in the presence of concentrated sulfuric acid in which the, raw reaction product is subjected to distillation, the step of adding to the raw reaction product a small amount of a phenol to prevent corrosion of the distillation equipment... 2. A-method according to claim 1 in which 3. A method according to claim 1 in which the phenol is tricresol.

4. A method according to claim 1 in which the phenol is-derived from petroleum.

5. In the alkylation of isoparamn with of concentrated sulfuric acid and the raw alkylate is subsequently distilled, the steps of treating 1 olefins where the reaction is carried out in the presence 

